Quite a similar sort of road to the Cat and Fiddle really, (i.e. very good but also very busy) The notorioty of the area means that you need to be on high alert for police pretty much continuously.
Fantastic road bordering Embalse de Sobrón. In the middle
of it you can visit the medieval City of Frias.
In Trespaderne you can choose to go to the medieval town of Medina de Pomar, going north to Bilbao through another fantastic road, or going west to Santander through another panoramic road following Ebro river.
I found this a really nice ride through vineyards of Rioja on an essentially empty road.